The microstructural evolution of water ice in the solar system through sintering

TL;DR

This study models the microstructural evolution of water ice in the solar system through sintering, assessing its rate, effects, and implications for planetary surface evolution, highlighting temperature and grain size sensitivities.

Contribution

It evaluates the applicability of the Swinkels and Ashby sintering model to water ice, comparing predictions with observations and identifying key factors influencing sintering timescales.

Findings

Ice can undergo significant microstructural changes over geologic timescales.

Sintering rates are highly sensitive to temperature and grain size.

Densification occurs over longer timescales, affecting surface porosity and cohesion.

Abstract

Ice sintering is a form of metamorphism that drives the microstructural evolution of an aggregate of grains through surface and volume diffusion. This leads to an increase in the grain-to-grain contact area ("neck") and density of the aggregate over time, resulting in the evolution of its strength, porosity, thermal conductivity, and other properties. This process plays an important role in the evolution of icy planetary surfaces, though its rate and nature are not well constrained. In this study, we explore the model of Swinkels and Ashby (1981), and assess the extent to which it can be used to quantify sintering timescales for water ice. We compare predicted neck growth rates to new and historical observations of ice sintering, and find agreement to some studies at the order of magnitude level. First-order estimates of neck growth timescales on planetary surfaces show that ice may undergo significant modification over geologic timescales, even in the outer solar system. Densification occurs over much longer timescales, suggesting some surfaces may develop cohesive, but porous, crusts. Sintering rates are extremely sensitive to temperature and grain size, occurring faster in warmer aggregates of smaller grains. This suggests that the microstructural evolution of ices may vary not only throughout the solar system, but also spatially across the surface and in the near-surface of a given body. Our experimental observations of complex grain growth and mass redistribution in ice aggregates point to components of the model that may benefit from improvement, and areas where additional laboratory studies are needed.